Studying the Occurrence of Pc5 ULF waves and their Spatio-temporal Characteristics Using SuperDARN

Ultralow frequency (ULF, ~2mHz-5Hz) magnetohydrodynamic waves are ubiquitous in Earth's magnetosphere and are driven by a range of mechanisms with energy sources both internal and external to it. ULF waves are an important coupling mechanism between the solar wind, magnetosphere, and ionosphere. ULF waves in the Pc5 band (~1.7-6.7mHz) play significant roles in the solar-terrestrial energy pathway as well as in radiation belt dynamics, namely the radial diffusion of energetic electron populations.

The coherent-scatter radars in the SuperDARN network are ideal for the study of ULF waves. In radar backscatter, ULF waves are identified as periodic oscillations in the line-of-sight Doppler velocities of field-aligned plasma irregularities in the upper-ionosphere. These oscillations are explained as ExB drift fluctuations induced by the waves' electric field component. SuperDARN radars offer wide and fixed fields-of-view, a relatively fine spatial resolution compared to ground magnetometers, and a 60s temporal resolution, thus facilitating the observation of Pc5 waves with a wide range of scale sizes as well as of their propagation characteristics.

Here we present statistical work on the occurrence of Pc5 waves observed in the common mode backscatter recorded by the Hankasalmi SuperDARN radar throughout the years 2013-14 as well as that of their spatio-temporal characteristics. Over 200 discrete wave events are included. The distribution of and the relationships between a number of their propagation, spectral, and spatial characteristics are considered, as well as their relationships to solar wind drivers.